1. Field of the Invention
The present invention is broadly concerned with adhesives which are particularly suited for use in sealing metallic joints in automobiles, appliances or other metallic structure. More particularly, the invention is concerned with an improved adhesive which includes a permanently magnetized substance within the adhesive for giving the latter a substantially permanent, net magnetic field. The invention also comprehends a method of making the improved magnetized adhesive, and to a method of sealing joints through the use thereof. 2. Description of the Prior Art
Various types of adhesives have long been used in the automotive and appliance industry for sealing metallic joints. For example, an adhesive seal is commonly provided along the joint between an automobile fender and the adjacent structural member. The conventional practice in this regard has been to apply a flowable, viscous adhesive along the joint through the use of an appropriate applicator, whereupon the adhesive is allowed to set. Although this technique is feasible where a given joint is easily accessible and the adhesive is applied atop the joint, severe problems are encountered when the joint is inaccessible or where adhesive must be applied to the underside of the joint, as in the case of an automobile fender seal. In such instances it often occurs that the operator, because of inaccessibility of the joint, misapplies the viscous adhesive and in effect "misses" the joint. This necessitates a further application of the adhesive, since after application thereof it is impractical to attempt to shift or otherwise move the adhesive. This of course leads to an excess of adhesive being applied adjacent the joint, which is both costly and unnecessary. In addition, when adhesive is applied to the underside of a joint, the adhesive has a tendency to "sag" under the influence of gravity, and this of course detracts from the integrity of the seal. This problem is also encountered when the automobile or appliance is passed through a curing oven, or when, in use, the metallic joint is subjected to unusual heating. In such cases the adhesive disposed along the underside of the joint will again tend to become partially flowable, and can at this point "sag" as described above.
For all of the above reasons, there is a decided need for an improved adhesive which can be placed by hand or otherwise along a joint, and thereafter be shifted as necessary to assure proper positioning of the adhesive, and which overcomes the problem of adhesive "sag" inherent with most types of conventional adhesives.
U.S. Pat. No. 2,393,541 describes an adhesive which includes finely divided metal particles or alloys having ferro-magnetic properties dispersed therein. Therein adhesives are applied to a nonmetallic joint to be sealed, and are placed in a high frequency electromagnetic field which serves to heat the dispersed particles, and thereby the adhesive itself, by virtue of the well known hysteresis effect. However, Pat. No. 2,393,541 does not describe any adhesive having a permanently magnetized substance therein which gives the adhesive a substantially permanent, net magnetic field. Indeed, this patent is specifically described for use in conjunction with wooden joints, as opposed to those of a metallic variety.
Other patents describing adhesives containing particles subject to hysteresis heating include the following: U.S. Pat. Nos. 2,087,480, 3,249,653, 3,620,875, 3,840,254, 3,959,537 and 4,035,547. The teachings of all of these patents are distinguishable from the present invention on the same basis as outlined above in connection with Pat. No. 2,393,541.
U.S. Pat. No. 2,712,219 describes a process for sealing cartons wherein a filled carton is provided with a metallic insert adjacent the upper end thereof. The carton closure flaps are then folded over the insert, with glue being applied between the flaps. This construction is then passed under an electromagnet which pulls the carton upwards to compress the closure flaps between the magnetic insert and the electromagnet, thus effecting bonding of the closure flaps. This patent also mentions that in lieu of the magnetic insert a material for the same purpose can be sprayed onto the sealing flaps, either as a part of the adhesive or as an underlying layer. Again, however, U.S. Pat. No. 2,712,209 does not describe an adhesive which is so formulated to have a substantially permanent, net magnetic field before and during use thereof.
The following patents are of background interest only to the present invention and relate to iron surface coatings, paints, ion exchange resin beads and coating compositions. None of these patents deal with adhesives, however: U.S. Pat. Nos. 3,709,730, 3,766,074, 3,977,984 and 4,049,566.